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  • Motorcycle machining work

    A friend of mine who is restoring a 1956 Royal Enfield motorcycle came by today and brought me a project. The original sprocket was worn out (look at the pointed teeth). The "original" sprocket looks pretty suspect---It seems to have been bored out at some time in the past to fit the hub on his rear wheel, and the bore is definitely not concentric to the outer diameter of the bored hub. He bought this motorcycle in pieces in a basket, and has spent all winter refurbishing and rebuilding, and trying to figure out how it all goes together. The bike is a transition model. It's not quite a 1955 model, but it's apparently not the full production 1956 model either. He purchased another sprocket and hub, which is very close to his original, but the bore is about .040" smaller than the "thru bore" on his worn out sprocket, and about 5/16" too long. I am going to attempt to bore the hub out to spec and shorten it the required amount. When I bore something on the lathe, I never quite trust the inside gauges I have to tell the absolute truth. I like to try whatever is going to fit into the bore for final fit before tearing down my set-up. Since the tire and wheel are far too large to "trial fit" the first operation was to take a piece of aluminum I had on hand and turn it to the same diameter as the hub in the tire and wheel assembly. The last picture shows the old sprocket and hub setting in place on the aluminum part that I made. Now I can tear down my set-up, and figure out if I am going to mount the sprocket and hub which needs to be bored on my faceplate or in my four jaw chuck.


    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

  • #2
    And the last two pictures show the aluminum piece I turned for my "trial fitting" and the old worn out sprocket/hub setting on it in the lathe.

    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #3
      Looks like it's going to be a faceplate job. The side of the sprocket/hub that I want next to the chuck has a large projection on it that prevents me getting a decent grip on it with the jaws of the four jaw chuck. I can't flip the part over and grip it from inside the brake drum because I need access to the brake drum surface to center things. I know that the sprocket is concentric to the brake drum, but I'm not sure that the outside diameter of the hub is concentric to the brake drum, so I can't center off it.
      Last edited by brian Rupnow; 04-01-2017, 07:03 PM.
      Brian Rupnow
      Design engineer
      Barrie, Ontario, Canada

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      • #4
        Originally posted by brian Rupnow View Post

        Hmmmmm - kinda upset, Hosie told me he was booked up for welding anything till mid July

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        • #5
          Originally posted by A.K. Boomer View Post
          Hmmmmm - kinda upset, Hosie told me he was booked up for welding anything till mid July
          Could be a bird infestation issue ;-)
          If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

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          • #6
            lol --- there's only one man in the world that I know of who can "throw down" those kinds of welds

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            • #7
              how about turning a ring you can bolt to the hub using those three slots, and grip in the 4 jaw? Shim those projections so it's true.

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              • #8
                Originally posted by kendall View Post
                how about turning a ring you can bolt to the hub using those three slots, and grip in the 4 jaw? Shim those projections so it's true.
                Kendall--that suggestion has a lot of merit. If I don't do that, I will have to drill and tap holes in my faceplate. The "bolt pattern" of the 3 slots is smaller than the slots in my faceplate.
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

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                • #9
                  Brian - Can you set it up in the mill and use the boring head?
                  Larry - west coast of Canada

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                  • #10
                    Faceplates are" Consumable items"

                    Originally posted by Cuttings View Post
                    Brian - Can you set it up in the mill and use the boring head?
                    Drilling and tapping holes in a faceplate is not a sin. If it lets you USE the faceplate for a job you otherwise could not do then do not worry. Regards David Powell;

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                    • #11
                      Cuttings--Great minds think alike.--I have been studying on this thing for a couple of hours, and I don't see any way of mounting it in the lathe without making at least one fixture to attach it to the faceplate or grip it with the 4 jaw chuck. if I set it up in the mill on some 1 2 3 blocks for spacers and use some toe clamps I can center off the inside of the brake drum for boring, and also access the end that I have to take 5/16" off. The thru bore of the hub is only 2.66", and the stroke on my mill quill is 2.9".
                      I only have to take a very small amount out of the bore, and the bore isn't going to be a bearing surface, just a centering surface. My longer brazed carbide boring bar is long enough and stout enough to do this. I'm trying to think of a downside to this, and I really can't see one.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • #12
                        Originally posted by David Powell View Post
                        Drilling and tapping holes in a faceplate is not a sin. If it lets you USE the faceplate for a job you otherwise could not do then do not worry. Regards David Powell;
                        David---I really have nothing against drilling and tapping holes in the faceplate. It's more a matter of having to build a special fixture to enable me to use the faceplate that is making me consider doing it on the mill.
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

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                        • #13
                          For future reference in case it hadn't occurred to you, you could have made a new set off tall jaws for your 4 jaw chuck.

                          I prefer making precision bores in the lathe rather than with a boring head. Boring heads have a tendency to "jump" when micro adjusting unless you have a really good one.

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                          • #14
                            You do know that they still make Royal Enfield motorcycles? More than likely get a new one from India, factory direct.

                            As soon as I sell my Suzuki, I'm in the market for one of the new ones, old school looks, fuel injected modern bits, cheap to run. What's not to like...?

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                            • #15
                              Hitchcocks Motorcycles, Solihull, England, UK.
                              Got EVERYTHING Royal Enfield.
                              Check their website and on line catalogue out.
                              Those slots are for part of the cush drive system.
                              Those one piece brake drum and sprocket systems are a pain in the ar$e.
                              Better to modify the rear drum to adapt a bolt on sprocket.
                              Hitchcocks sell rear drums for a bolt on sprkt (38 to 50T). Was only looking yesterday, hence my post on this thread.

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